THE FLOWER AND FRUIT 



95 



sessile on an elongated axis as in the carpellate flowers of Cannabis. 

 In the raceme, the flowers are pediceled on an elongated axis rather 

 than being sessile like the spike (Raphanus and Medicago). In 

 the head, the sessile flowers are closely aggregated on a shortened 

 axis (Lactuca and most Compositae). In the umbel, the lateral 

 axes bearing the flowers are approximately equal in length, each 

 one terminating in a flower. 



Where the lateral branches rebranch and each axis is terminated 

 by a flower, a panicle is formed. (Fig. 36.) Included in this 

 category are the true panicle; the compound panicle, or spike made up 

 of spikelets (Triticum); and, where the main axis is unelongated, 



Fig. j6. Types of inflorescences. A, cyme (diagrammatic); B, compound cyme of Sap- 

 onaria, after Rushby; C, panicle (diagrammatic). (From Smith, et al., Textbook of General 

 Botany.^ 



the compound umbel. In the compound umbel, each lateral axis is 

 terminated by a small umbellet bearing several flowers (Apium and 

 other members of the Umbelliferae). In the cyme, the branching is 

 sympodial and determinate. The inflorescence is usually broad 

 and flat, and the lateral axes terminate in flowers after producing 

 one or more branches of a second order which also bear flowers 

 CLinum"). 



Floral Types and Phylogeny. — The possibilities of variation 

 in floral types are almost unlimited. The most obvious of these 

 are variations in the color of the flower, and in the size, shape, 

 arrangement, and number of floral parts. Where the flowers are 

 cyclic, the most common floral plan is the pentacyclic one, in which 

 there are five sets of parts, these usually consisting of one cycle of 

 sepals, one of petals, two of stamens, and a central cycle of carpels. 

 In the tetracyclic arrangement, there is only one cycle of stamens. 

 Where the number of carpels is the same as the number of sepals and 



